I. Field of the Invention
This invention relates to synthetic speech and more particularly to a method of synthesising a digital waveform from signals representing phonemes.
II. Related Art and Other Considerations
There are many circumstances, e.g. in telephone systems, where it is convenient to use synthesised speech. In some applications the starting point is an electronic representation of conventional typography, eg. a disk produced by a word processor. Many stages of processing are needed to produce synthesised speech from such a starting point but, as a preliminary part of the processing, it is usual to convert the conventional text into a phonetic text. In this specification the signals representing such a phonetic text will be called xe2x80x9cphonemesxe2x80x9d. Thus this invention addresses the problem of converting the signals representing phonemes into a digital waveform. It will be appreciated that digital waveforms are common place in audio technology and digital-to-analogue converters and loud speakers are well known devices which enable digital waveforms to be converted into acoustic waveforms.
Many processes for converting phonemes into digital waveforms have been proposed and it is conventional to do this by means of a linked database comprising a large number of entries, each having an access portion defined in phonemes and an output portion containing the digital waveform corresponding to the access phonemes. Clearly all the phonemes should be represented in the access portions but it is also known to incorporate strings of phonemes in addition. However, existing systems only take into account the phoneme strings contained in the access portions and do not further take into account the context of the strings.
This invention, which is defined in the claims, uses a linked database to convert strings of phonemes into digital waveform but it also takes into account the context of the selected phoneme strings. The invention also comprises a novel form of database which facilitates the taking into account of the context and the invention also includes the method whereby the preferred database strings are selected from alternatives stored therein.